Catalysts are an important component of many chemical reactions as they typically increase the rate of the reaction. They may also inhibit the formation of competing products as there is less time for significant product formation by competing reactions. Beyond improving reaction rate and enhancing product yield, catalysts may also provide an enantioselective mechanism for obtaining an optically active product. Often an enantioselective catalyst is itself chiral and optically active. There is a need for the development of enantioselective catalysts to catalyze reactions resulting in optically active products. Many naturally occurring and biologically active molecules are optically active and many reaction mechanisms, especially biological reactions, only function with compounds having a specific enantiomeric configuration.
Polymeric catalysts may be useful in large-scale industrial applications. It is often easy to separate the polymeric catalyst from the products of the catalyzed reaction as a polymeric catalyst has special solubility properties because of its macromolecular nature. In addition, removal of the polymeric catalyst by filtration is typically enhanced because of the polymer's large size. Furthermore, studies have also shown that polymer-supported catalysts may have more durable catalytic activity than monomeric metal complexes. It is, however, often difficult to predict the activity of a polymeric catalysts from knowledge about the monomer.
A number of catalysts are organometallic species, which are formed by the combination of an organic molecule or polymer and a metallic compound, cation, or complex. Organozinc species are known catalysts in the alkylation of aldehydes, see reviews by Soai, et al., Chem. Rev., 92, 833 (1992) and Noyori, et al., Angew. Chem. Int. Ed. Engl., 30, 49 (1991) and the reduction of ketones, see review by Deloux, et al., Chem. Rev., 93, 763 (1993). Both monomeric and polymeric catalysts are known. However, the polymeric catalysts that have been studied are primarily known chiral catalysts of the reaction which are covalently bonded to an achiral polymeric backbone, such as polyethylene or polystyrene. See e.g., Soai, et al., Chem. Rev., 92, 833 (1992) and D. Seebach, Helvetica Chimica Acta, 79, 1710 (1996). A polymeric chiral catalyst with a backbone structure that is sterically regular could potentially provide better enantioselectivity or catalytic activity than chiral molecules merely attached as pendent groups on a polymer backbone.
Because of the enhanced reaction rate and decreased formation of side products, and, in the case of chiral catalysts, potential enhanced enantioselectivity, there is a need for the development of new catalysts which may provide improved reaction times, yields, or enantioselectivity to the reactions. Furthermore, there is a need for new catalysts which may be useful with a variety of substrates.